By using wasted and often unwanted vibrational energy, small-scale vibrational energy harvesters have the potential of powering embedded, remote, and portable low power electronic circuits, sensors, and transmitters independent from the mains power or from a battery. Medium-scale vibrational energy harvesters have the potential of powering lighting systems. Large scale vibrational energy harvesters have the potential of powering facilities, communities, cities and regions either with grid-interactive and grid-independent operation. However, the use of conventional piezoelectric benders for vibration energy harvesters has been limited due to their low energy output, high vibrational frequency requirement, and narrow frequency bandwidth.
Currently, micro-electro-mechanical systems (MEMS) and conventional vibrational energy harvesters develop microwatt and milliwatt power levels, respectively, limiting their usage to powering MEMS sensors, ultralow power wireless sensors, or ultralow power electronic devices.
As illustrated in prior art FIG. 1a, all commercial, all patented, and most likely all developmental piezoelectric based vibrational energy harvesters are based on the same conventional monolithic bimorph energy harvester 30 that comprises a cantilever beam 32 that is made up of two piezoelectric or electrostrictive plate elements 34, 36, or some slight variation of a cantilever beam and configuration. This configuration was first developed and modeled by Jacque Curie in 1889, shortly after the discovery of piezoelectricity in 1880. This bender's construction is identical with 1938-1958 Rochelle salt and 1950s-1970s ceramic phonograph cartridge construction. The materials utilized are based on commodity materials developed in the 1960s and classified by the Defense (see DoD-Std 1376B(sh)). This cantilever beam configuration has been shown to have a number of advantages, including relatively low resonance frequencies, relatively high level of average strain for a given force input, and relatively easy and cost-competitive micro-fabrication process. As piezoelectric-based technologies have proven high volume manufacturing success, these harvesters are considered mature and adequate. Likewise, others concluded that they have the highest probability and impact of success.
Whereas, prior art piezoelectric-based power generators have adequate voltage output (high g31), unfortunately they have suffered from low current output (d31) and thusly low power output (g31*d31) (see piezoelectricity standard ANSI/IEEE Std. 176-1987). As shown herein in FIG. 3, these prior art generators have low energy output except at high vibrational amplitudes, narrow frequency bandwidth, and low efficiency. Table 1 below shows on the left side the prior art energy output of various MEMS, small monolithic, and large monolithic bender devices.
The following is a summary of related art: U.S. Pat. No. 7,446,456 to Xu uses a curved piezoelectric sheet in a flextensional arrangement, which increases the force and therefore the power output, but the piezoelectric sheet operates in the lowest efficiency d31 mode.
U.S. Pat. No. 7,345,407 to Tanner uses plural cantilever bimorphs connected to a frame and the outputs of each element add up to produce more power. However, because these conventional bimorphs have low efficiency, when they are connected in parallel, this causes problems with one element discharging into the next. Therefore, each element must be wired or isolated which is complicated.
U.S. Pat. No. 7,293,411 to Fitch uses altering liquid distribution to improve the tuning of conventional bimorphs which have inherently low efficiency, wherein the tuning “tries” to maximize the output which can be accomplished either mechanically (per Fitch) or electrically. However, this will only marginally improve the bandwidth or efficiency.
U.S. Pat. No. 7,260,984 to Roundy uses a circular bimorph to harvest energy for tire pressure monitor powering. Pressure differentials in the tire versus tire rotation are utilized to harvest. This concept utilizes conventional circular bimorphs which have inherently low efficiency. U.S. Pat. No. 7,258,533 to Tanner uses a piezoelectric plate of film on a pump diaphragm to harvest energy. The film which bends similar to conventional bimorphs has inherently low efficiency.
U.S. Pat. No. 7,239,066 to Ott utilizes numerous cantilever benders in a rotating device while employing a rotator. This concept utilizes conventional cantilever benders, which have inherently low efficiency.
U.S. Pat. No. 7,208,845 to Masters uses a conventional cantilever bender to harvest energy from fluid flow, by using vortex shedding. This patent utilizes tuning of the vortex shedding to the bender with minimal flow obstruction. This concept utilizes conventional cantilever benders, but couples it to a vortex shedder.
U.S. Pat. No. 7,157,835 to Sakai uses a conventional piezoelectric bender while adding an oscillating device in order to increase mechanical motion to increase power. This concept utilizes conventional cantilever benders, which have inherently low efficiency. In addition, higher motion is provided, though the strength of the bender will limit the amount of motion amplification which can be utilized. This concept uses a different harvesting structure. However, this structure can only operate in a low efficiency mode. Also, no consideration was given to fabrication of these fibers. Fibers such as these have been proposed many times, but are thought to have never been fabricated successfully.
U.S. Pat. No. 6,994,762 to Clingman uses a single crystal piezoelectric bonded to a metal substrate in order to pre-stress the crystal. This concept utilizes single crystals rather than piezoelectric ceramic. The use of pre-stresses is well known from Paul Langevin's tonpilz (1917) to 1960s fiberglass wrapped sonar tubes to the modern Rainbow, Cerambow, and Thunder devices, which are well known.
U.S. Pat. No. 6,984,902 to Huang uses a magnetostrictive material bonded to two piezoelectric materials to make a composite transducer, which converts mechanical to electrical and mechanical to magnetic. This, however, creates a difficulty that each material has a different sign and that cancels the other unless harvested separately. In effect, this is the same as using two transducers together. In addition, due to its use of coils and permanent magnets, the magnetostrictive component will suffer from energy density.
U.S. Pat. No. 6,947,714 to Weiss uses a striker to hit conventional piezoelectric ceramic to generate energy. This concept is no different from a commercial impact igniter used for BBQ grills or gas appliances. Struck piezoelectrics can deliver high voltage, but very low current. A single piece of ceramic offers by itself low energy density. Therefore, the struck piezoelectric will have very low energy generation. In addition, the ceramic could not be struck quickly enough to generate much power. Striking is at a very low frequency compared with vibrations.
U.S. Pat. No. 6,938,311 to Tanielian uses a multiple MEMS cantilever bimorphs with multiple masses in order to have numerous natural resonance frequencies to increase bandwidth and power harvesting capability. If one conventional harvester is not efficient enough, produce enough energy, or have a wide enough bandwidth, then it is only obvious that more would be better. This is particularly true with MEMS based devices, which have very little output. Tanielian does not address the problem with low output from the harvester itself.
U.S. Pat. No. 6,858,970 to Malkin and its related U.S. Pat. No. 6,938,311, use an array of MEMS cantilever bimorphs with various masses in order to add the power generated from each bimorph at various resonances. Again, if one is not good enough, then more would be required.
U.S. Pat. No. 6,807,853 to Adamson which uses an inter-digitated 1:3 piezocomposite to harvest energy from tire rotation. This concept utilizes a different composite configuration to harvest energy. The inter-digitated 1:3 has slightly higher efficiency than a conventional bender, but will suffer from lower capacitance. Therefore, there will be greater bandwidth or ability to capture a wider range of mechanical vibration frequencies at a lower current level. As such, it has been shown that little to no improvement in energy density has been realized. The main advantage, however, is reliability or durability, albeit at a higher component cost, of which conventional harvesters would require.
U.S. Pat. No. 6,771,007 to Tanielian utilizes an array of MEMS cantilever bimorphs, as do U.S. Pat. Nos. 6,938,311 and 6,858,970, where more bimorphs are required to get more output.
U.S. Pat. No. 6,725,713 to Adamson uses an inter-digitated 1:3 piezocomposite to harvest energy from tire rotation. Related to U.S. Pat. No. 6,807,853, this concept utilizes a different composite configuration, the inter-digitated 1:3 piezoelectric composite, to harvest energy.
U.S. Pat. No. 6,424,079 to Carroll uses an undulating piezoelectric polymer, which captures mechanical energy in fluid flow through the vortexes which form due to flow over an upstream bluff body. This concept utilizes a polymer piezoelectric material, which has at least two orders of magnitude lower in power generation than the ceramic material vortexes in the fluid flow are setup to capture fluid energy.
U.S. Pat. No. 6,407,484 to Oliver uses a Class IV flextensional amplified piezoelectric ceramic to harvest energy. This concept utilizes a single or stacked Class IV flextensionals to harvest energy, which amplify stresses by approximately 4 times, and therefore provides higher power generation, which is very low for a monolithic ceramic. This technology dates back to the early days of piezoelectric technologies first done by Hayes in U.S. Pat. No. 2,064,911.
U.S. Pat. No. 6,194,815 uses a rotor with numerous piezoelectric polymer blades. This concept utilizes a polymer piezoelectric material, which is at least two orders of magnitude lower in power generation than the ceramic material. The invention here is how to capture rotational energy, which is different.
U.S. Pat. No. 5,934,882 to Olney uses a ball or oscillating striker to impact a conventional piezoelectric bimorph or multilayer device to generate energy. This concept utilizes conventional piezoelectric elements. Olney uses striker mechanisms. However, strikes or impacts produce high voltage, but low current and power, as is utilized in gas igniters. Also, the impact can seriously degrade and/or damage the material over time.
U.S. Pat. No. 5,835,996 to Hashimoto uses a rotator to impact and vibrate conventional piezoelectric elements. The elements appear to be configured as a transformer in order to gain higher voltages. This concept utilizes conventional piezoelectric elements. Though the efficiency is higher using thickness mode, it suffers by being transformed. Also, the capacitance is low and therefore so is the power generation.
U.S. Pat. No. 5,801,475 to Kimura uses a conventional piezoelectric bender which is attached to a harvesting chip. This concept utilizes a conventional harvester having a hybrid or attachment with Si-based chip. U.S. Pat. No. 5,751,091 Takahashi utilizes a conventional triangular bender which is coupled to a rotating ratchet where the triangular shape, which is well known to reduce cross-coupling through the plane of the bender.
U.S. Pat. No. 5,729,077 to Newnham uses a Class IV flextensional amplified piezoelectric ceramic with different cap or shell designs to harvest energy. This patent is related to U.S. Pat. Nos. 5,276,657 and 4,999,819 with different cap or shell designs. This concept utilizes a single or stacked Class IV flextensionals to harvest energy, which amplify stresses by approximately 4 times, and therefore provides higher power generation, which is very low for a monolithic ceramic. From the Oyster transducer patented in 1964, Newnham has taken out the mechanical attachment using a prestressing bolt and replaced it with glue joints.
U.S. Pat. No. 5,512,795 to Epstein uses a piezoelectric polymer squeezed between two rotors that utilizes a polymer film, which is at least two orders of magnitude lower power output than ceramic.
U.S. Pat. No. 5,276,657 also to Newnham uses a Class IV flextensional amplified piezoelectric ceramic to harvest energy, which is related to U.S. Pat. Nos. 5,729,077 and 4,999,819, which utilize single or stacked Class IV flextensionals to harvest energy, with a simple cap or shell design.
U.S. Pat. No. 4,999,819 to Newnham the concept uses a Class IV flextensional amplified piezoelectric ceramic to harvest energy. Related to U.S. Pat. Nos. 5,729,077 and 5,276,657, this concept utilizes a single or stacked Class IV flextensionals to harvest energy, with a simple cap or shell design.
U.S. Pat. No. 4,467,236 to Kolm uses tuned conventional rectangular or circular benders to harvest energy from the gas flow of an engine exhaust. Kolm tunes to the air flow.
U.S. Pat. No. 4,387,318 which uses an array of piezoelectric fans to generate power from air flow or wind. This '318 patent uses a piezoelectric fan in reverse resulting in a conventional bender utilized to generate low power levels.
U.S. Pat. Appl. No. 2006/0021261 to Face uses a flextensional element or one of the various bender configurations (unimorph, bimorph, Rainbow, or Thunder) to harvest footfall energy within a shoe where only the incorporation of conventional commercially available piezoelectric components are within the shoe.
U.S. Pat. Appl. No. 2006/0129147 to Thiesen uses a conventional bimorph bender with an adjustable resonance frequency due to electrostatic or electromagnetic attraction/repulsion. Thiesen couples electrostatics or electromagnetics to adjust the resonances of a conventional bender.
U.S. Pat. Appl. No. 2007/0263887 to Tanner uses a spring loaded precurved bender, probably used to lower the resonance frequency. Tanner uses the spring loading to lower the frequency.
U.S. Pat. Appl. No. 2008/0129153 to Roundy uses a mass spring loading technique to lower the resonance frequency of a conventional bimorph bender. Roundy uses the mass-spring loading to lower the frequency.
U.S. Pat. Appl. No. 2008/0246367 to Fochtman uses a conventional bender, whose surface has been modified with ridges, grooves, or holes, in order to modify the sheet stiffness and the device resonance. Changing the surface structure of the piezoelectric allows a modest degree of tuning of the stiffness and resonance of conventional benders. However, this modification would be expensive and could negatively impact reliability. Other techniques such as mass-springs would appear to be a lower cost solution.
Therefore, what is sought is a vibration energy harvester that is capable of producing significantly higher power output than comparable conventional vibration energy harvesters.